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  • Hi, this is Henry, and this is the first in a series of videos about special relativity

  • This is definitely not an academic course,

  • but it's going to be a more in-depth and developed exploration of a single topic

  • than a typical standalone minute physics video.

  • I've been greatly inspired and heckled to do this by my friend Grant Sanderson of Three Blue One Brown

  • who set the standard for this kind of thing with his excellent series

  • series'es? on calculus and linear algebra.

  • So, special relativity.

  • Special relativity is one of the most popularly famous ideas in physics

  • It's the thing that Einstein figured out about the speed of light and space and time and e equals mc-squared

  • It changed our understanding of the universe and its core ideas are accessible in principle to anyone who understands some basic algebra and geometry

  • You don't even need to know calculus

  • And yet in spite of this

  • special relativity is one of the subjects in physics that confuses the most people and in many cases turns them away from physics altogether I

  • think in part

  • This is because special relativity is not quite a big enough subject to ever get its own full class in physics departments you might see

  • classical mechanics or quantum mechanics or electromagnetism or intro to general relativity on a course syllabus

  • But it's surprisingly rare to see special relativity

  • Even though relativity is an essential building block upon which most of the rest of modern physics depends

  • Special relativity is typically relegated to just a few days squeezed into the beginning or end of other physics courses.

  • However, the more important reason special relativity confuses so many people is that it's almost always introduced

  • confusingly with lots of complicated algebraic equations with Delta X's and Delta X Prime's and square roots

  • Which sometimes you divide by and sometimes you multiply by and all the while you're scrambling to figure out where in all this symbol logical

  • mess they're hiding a supposedly mind-blowing insight about the fundamental nature of space and time

  • Special relativity

  • doesn't have to be that way.

  • And I think the complicated explanations have only survived this long because they're how Einstein did it. But he was a professional

  • physicist climbing an intellectual mountain up its steepest face.

  • And I don't think that we should require everyone who learns about special relativity now to have to follow the same path Einstein did

  • Especially not now that we have super beautiful and simple geometric ways of explaining it

  • Essentially we figured out afterwards that there's a much easier way to climb the mountain than what Einstein did, a way that you could probably

  • even figure out on your own, given the right prompting. And it's that

  • fundamentally beautiful simple geometric way to understand space and time that I want you to leave with after watching this series of videos.

  • If all goes well, hopefully you'll gain some intuition for what special relativity really is, why it works

  • why it's right, and why all those paradoxes you've probably heard about aren't paradoxical at all.

  • They're just easy confusions to stumble into when you're attacking things with an army of square roots

  • This is going to require some mental effort from your end.

  • There's a very real

  • mathematical sense in which learning special relativity is kind of like living your entire life thinking the earth is flat

  • And then learning that the earth is actually round. A round Earth isn't actually that complicated of a thing to picture

  • I mean, it's just a ball

  • But trying to get used to that idea, to really take it in and figure out how your day-to-day

  • experiences on this flat seeming surface of the earth-- how they fit into this new round earth idea-- that would certainly take some mental effort.

  • It is, though, a totally different kind of mental effort from plugging lots of numbers into complicated square root formulas and

  • ultimately, much more worthwhile

  • I mean you probably have a pretty good intuition about round Earth concepts, like what happens if you just keep walking east and

  • what's the shape of the Earth's shadow on the moon without having to do complicated calculations in spherical polar

  • coordinates. In fact we're gonna take this analogy to the extreme.

  • Just like a globe is a really useful

  • hands-on visual way to explore what it means for the earth to be round because a globe comes with roundness built-in,

  • I've designed and had built a hands-on

  • space-time globe that has special relativity built in.

  • It's not quite as simple as a globe globe because special relativity is a little weirder than roundness

  • But the thing I like about this machined aluminum space-time globe is that it's a physical

  • manifestation of the intuition that I hope you develop for special relativity.

  • We're going to use it to gain a hands-on understanding of the twins paradox, length contraction, and time dilation,

  • why nothing can go faster than light, and much more. I hope to see you in the next video

  • And while you're waiting for the next special relativity video to come out you might want to check out this video's sponsor:

  • a site full of interactive quizzes and mini courses on physics and math. As you've probably heard me say before, if you want to

  • understand physics deeply, you really have to think through ideas and solve problems yourself and Brilliant offers a great way to do just that--

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Hi, this is Henry, and this is the first in a series of videos about special relativity


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B2 中上級

なぜ相対性理論は難しいのか?| 特殊相対性理論|特殊相対性理論 第1章 (Why is Relativity Hard? | Special Relativity Chapter 1)

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    林宜悉 に公開 2021 年 01 月 14 日